Shrink labels represent a high proportion of labelling applications. High shrink labels are the fastest growing segment in the labelling business due to the trend toward using contoured containers and shrink sleeve labels with 360° graphics for high customer appeal.
Application of heat to a shrink label around a contour container causes the label to shrink preferentially in the direction extending circumferentially around the container to conform to the outside container shape.
Shrink labels fall into two categories: roll-on-shrink-on (ROSO) labels and sleeve labels. ROSO labels are supplied from a reel, cut into sheets, applied around a container and seamed around the container during the labelling step using hot melt to form a seam, with the machine direction (MD) of the film extending circumferentially around the container. ROSO label films primarily shrink in the MD direction and generally employ biaxially oriented polypropylene (BOPP) films.
In contrast sleeve labels are solvent seamed into a tube and supplied from that tube placed around a container, with the transverse direction (TD) of the film extending circumferentially around the container. Application of heat causes the label to shrink preferably in the direction extending circumferentially around the container and to conform to the container. Sleeve labels primarily shrink in the TD direction.
Current high shrink sleeve labels are sleeves made of a TD shrink film that is solvent seamed into a folded tube. These high shrink labels provide more than 60% shrinkage and are usually made of polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene terephthalate glycol (PETG), polylactic acid (PLA) or oriented polystyrene (OPS). PVC and PET labels are not easily separated from PET bottle flakes using the flotation technique in the recycling process as the films have a density higher than 1 kg/dm3. OPS film requires transportation and storage under controlled conditions due to high natural shrinkage phenomenon occurring gradually at a storage temperature in a warehouse. Natural shrinkage causes deformation problems in a roll form.
While ROSO labels offer a cost advantage, the sleeve labels enjoy an advantage in the extent of shrink percentage that can be obtained. Sleeve labels typically shrink up to 60-70% around the circumference of the container whereas commercial ROSO films shrink only up to 20%.
Currently, no “all polyolefin” shrink films are known to be solvent seamed to form a tube, due to the inability of solvent to swell semi-crystalline materials. Solvent sealable material like polystyrene (PS) or PET may be coextruded on the polyolefin based film, but it will require an expensive tie layer to bond the solvent sealable skin on the polyolefin core layer. Such combination of a solvent sealable skin on a polyolefin core layer using an adhesive tie layer has other disadvantages like the development of haze on film after shrinkage or poor optics when the film is recycled.
It is therefore desirable to identify a polyolefin based film suitable for sleeve labelling that can be seamed on the current available solvent seamed machines and shrink around a container to at least 50%, has low natural shrinkage and can be easily separated from PET flakes for recycling. Shrinkage in a steam tunnel for high heat efficiency would be preferred.
WO2006/071826 discloses multilayer heat shrink film having a core layer comprising a blend of (i) at least one polyterpene and (ii) a syndiotactic polypropylene or a cyclic olefin copolymer (COC) and skin layers comprising one or more polyolefins having an ultimate shrinkage of at least 25% at 135° C. These films suffer from low stability and stiffness.
EP 1632343 discloses a multilayer heat shrinkable film composed of at least three layers comprising skin layers made of resin composition comprising 55 to 95% by mass of cyclic olefin based resin and from 45 to 5% by mass of a linear low-density polyethylene and an intermediate layer composed of a resin composition comprising 95 to 55% by mass of propylene-α-olefin random copolymer and from 5 to 45% by mass of the cyclic olefin based resin. The density and cost of such films are high.
It has now been discovered that combining a polyolefin core layer with one or two skin layers composed of solvent sealable or swellable polymer such as cyclic olefin copolymer (COC) provides a film that can be used for shrink sleeve labelling with up to about 70% shrink at temperature compatible with steam tunnel. The COC is solvent sealable using the standard solvent used in sleeve labelling. The films and/or labels made from the films have high stiffness for good dispensing. Their low natural shrinkage provides good storage stability and usually avoids transportation and storage under controlled conditions. Finally the multilayer films according to the disclosure are particularly suitable to produce labels that are easily separated from the PET containers.